To further understand the transmission and colonization of periodontopathic microorganisms, the degree of intrafamily concordance of oral strains of Actinomyces viscosus and naeslundii is being determined by testing subgingival plaque samples of individual family members with specific monoclonal antibodies and immunofluorescence. The ability to "fingerprint" specific bacterial substrains found in dental plaque with monoclonal antibodies provides an epidemiological tool to study the transmissibility of microorganisms within families. A finding of significant familial clustering will imply that members of the same family tend to be more alike with respect to a particular strain of bacteria (Actinomyces) than individuals from different families, which is characteristics of many infectious and transmissible diseases.